In the case of semiconductor devices, a lack of adhesion between a system carrier and the plastic housing composition has the effect that moisture accumulates in the boundary layer between system carrier and plastic housing composition. The moisture expands abruptly if the semiconductor device is heated from room temperature to temperatures of up to 260° C. in a very short time during soldering onto a printed circuit board. The consequence of the abrupt expansion of the moisture content is cracks and/or fractures in the plastic housing of the semiconductor device, which is referred to as the “popcorn effect”.
In order to prevent this popcorn effect, it is necessary to prevent the accumulation of moisture in the boundary layer between semiconductor device components and plastic housing composition. The accumulation of moisture can be reduced by improving the adhesion between the surfaces of the semiconductor device components and the surface of the plastic housing composition. Various approaches are known for improving the adhesion. U.S. Pat. No. 5,554,569 discloses a method for mechanically roughening the surface of a leadframe. The roughened surface enables an intermeshing with the plastic housing composition and consequently a better adhesion. However, this method is cost-intensive and difficult to carry out.
In the document H. Y. Lee et al. “Failure paths at copper-base leadframe/epoxy moulding compound interfaces”, Journal of Material Science 37, 2002, pages 4247 to 4257, copper(II)oxide and copper(I)oxide layers are produced in a hot sodium hydroxide solution on leadframes made of copper and their adhesion promoting properties with respect to a plastic housing composition are investigated, transference to the practical fabrication of semiconductor devices not being unproblematic since here the adhesion promoting layer is based on wet-chemical techniques, which does not reduce the risk of moisture inclusions.
In the document Kilwon Cho et al. “Effect of the microstructure of copper oxide on the adhesion behaviour of epoxy/copper leadframe joints”, J. Adhesion Sci. Technol., Vol. 14, pages 1333 to 1353, (2000), laminae made of copper are thermally oxidized and copper(II)oxide and copper(I)oxide layers are produced and their adhesion promoting properties with respect to a plastic housing composition are investigated. It is pointed here that with increasing thermal oxidation, a conversion from copper(I)oxide to copper(II)oxide takes place and this conversion enables adhesion promotion with respect to a plastic housing composition, which has been problematic hitherto in the case of pure copper surfaces and/or in the case of surfaces with a copper(I)oxide layer, for which reason leadframes made of an iron-nickel alloy including 42% by weight nickel have been used hitherto, the thermal oxides of which ensure the adhesion to a plastic housing composition in an improved fashion.
There is a need, however, in the further development of the semiconductor devices, to increase the interface stability and the adhesiveness between the widespread plastic housing composition made of filled epoxy resins and the leadframe in order to improve the service life and the reliability of the semiconductor devices, and at the same time to minimize the costs, especially as the alloy costs of the iron-nickel leadframes are relatively high. Moreover, there is a need to improve the electrical conductivity of the leadframes with respect to iron-nickel leadframes. However, the thermal copper(I)oxides are known as a weak point in the embedding of semiconductor device components into a plastic housing composition. A further disadvantage is that thermal copper oxides on the leads of a copper leadframe impede a bonding connection.